The investigator proposes to define sequences in the HIV env gene that are responsive to host cell control. This will be attempted by deleting sequences in the env gene and determining the effects of these deletions on viral RNA localization. In addition, the investigator proposes to add sequences from env and gag (specifies virion core proteins) genes to heterologous genes. After defining minimal sequences that prevent cytoplasmic accumulation of viral RNA in COS cells, the applicant will try to determine directly whether or not there is a role for these sequences on the efficiency of RNA splicing and whether or not there is a role for these sequences on RNA stability. Another aspect of this project is to try to characterize the mechanism by which env protein production is suppressed in the absence of Rev and to determine how Rev overcomes this suppression in HeLa cells. Additionally, the investigator proposes to determine the differences between the regulation of env RNA in COS and HeLa cells that account for differences in RNA localization in these two cell types. Dr. Emerman also will try to test a variety of other cell types for their regulation of env RNA localization. The applicant has developed a novel cell line for determination of viral titers. This cell line will be used to determine the effects of over-expression of each of the HIV regulatory genes on virus growth in lymphocytes. Quantification of viral spread through these cell lines may allow the determination of which steps of the virus life cycle are limiting and whether or not replication of virus can be hindered by inappropriate temporal expression of its regulatory genes.